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gfdl's home page > gfdl on-line bibliography > 2001: Journal of Physical Oceanography, 31(2), 554-571
The scales and equilibration of midocean eddies: Freely evolving flow
| Smith, K. S., and G. K. Vallis, 2001: The scales and equilibration of midocean eddies: Freely evolving flow. Journal of Physical Oceanography, 31(2), 554-571. |
Abstract: Quasigeostrophic turbulence theory and
numerical simulation are used to study the mechanisms determining the
scale, structure, and equilibration of mesoscale ocean eddies. The
present work concentrates on using freely decaying geostrophic
turbulence to understand and explain the vertical and horizontal flow of
energy through a stratified, horizontally homogenous geostrophic
fluid. It is found that the stratification profile, in particular
the presence of pycnocline, has significant, qualitative effects on the
efficiency and spectral pathways of energy flow. Specifically,
with uniform stratification, energy in high baroclinic modes transfers
directly, quickly (within a few eddy turnaround times), and almost
completely to the barotropic mode. By contrast, in the presence of
oceanlike stratification, kinetic energy in high baroclinic modes
transfers intermediately to the first baroclinic mode, whence it
transfers inefficiently (and incompletely) to the barotropic mode.
The efficiency of transfer to the barotropic mode is reduced as the
pycnocline is made increasingly thin, The
effect, on the other hand, improves the efficiency of barotropization,
but for oceanically realistic parameters this effect is relatively
unimportant compared to the effects of nonuniform stratification.
Finally, the nature of turbulent cascade dynamics is such as to lead to
a concentration of first baroclinic mode kinetic energy near the first
radius of deformation, which, in the case of a nonuniform and
oceanically realistic stratification, has a significant projection at
the surface. This may in part explain recent observations of
surface eddy scales by TOPEX/Poseidon satellite altimetry, which
indicate a correlation of surface-height variance with the scale of the
first deformation radius. |